Fuel cell power plants include fuel gas steam reformers which are operable to catalytically convert a fuel gas, such as natural gas or heavier hydrocarbons, into the primary constituents of hydrogen and carbon dioxide. The conversion involves passing a mixture of the fuel gas and steam through a catalytic bed which is heated to a reforming temperature which varies depending upon the fuel being reformed. Catalysts typically used are nickel catalysts which are deposited on alumina pellets. There are three types of reformers most commonly used for providing a hydrogen-rich gas stream to fuel cell power plants. In addition, hydrocarbon fuels may be converted a hydrogen-rich gas stream by use of a partial oxidation reaction apparatus. These are a tubular thermal steam reformer, an autothermal reformer, and a catalyzed wall reformer. A typical tubular thermal steam reformer will consist of a plurality of reaction tubes which are contained in a housing that is insulated for heat retention. The reaction tubes are heated by burning excess fuel gas in the housing and passing the burner gas over the reaction tubes. The reforming temperature is in the range of about 1,250.degree. F. to about 1,600.degree. F. The individual reaction tubes will typically include a central exhaust passage surrounded by an annular entry passage. The entry passage is filled with the catalyzed alumina pellets, and a fuel gas-steam manifold is operable to deliver the fuel gas-steam mixture to the bottom of each of the entry passages whereupon the fuel gas-steam mixture flows through the catalyst beds. The resultant heated mixture of mostly hydrogen and carbon dioxide gas then flows through the central exhaust passages in each tube so as to assist in heating the inner portions of each of the annular catalyst beds; and thence from the reformer for further processing and utilization.
A typical autothermal reformer may be a single bed or a multiple bed tubular assembly. Autothermal reformers are often used when higher operation temperatures are required for the reforming process because the fuel to be processed is more difficult to reform. In an autothermal reformer, the reaction gasses are heated by burning excess fuel within the reaction bed by adding air to the fuel and steam mixture so that the remaining fuel-steam mixture is increased to the temperature necessary for the fuel processing reaction. Typically, wall temperatures in an autothermal reformer are in the range of about 1,400.degree. F. to about 1,800.degree. F. Such tubular reformers are disclosed in U.S. Pat. No. 4,098,587.
A third type of prior art reformers have utilized catalyzed wall passages such as disclosed in U.S. Pat. No. 5,733,347. Such reformers are formed from a sandwich of essentially flat plates with intervening corrugated plates which form reformer gas passages and adjacent regenerator-heat exchanger passages. Each of the reformer passage plate units is disposed directly adjacent to a burner passage plate unit so that the adjacent reformer and burner passages share a common wall.
Besides the reformer devices described above, a partial oxidation reaction apparatus may also be used to produce a hydrogen-rich fuel stream. This device is typically a chamber that is fed a hydrocarbon fuel, steam and oxidant source, usually air, so that the mixture spontaneously partially oxidizes to form a hydrogen-rich mixture. Such devices, for example, are disclosed in PGT application WO 98/08771.
Each of the aforesaid prior art reformer structures may suffer from carbon buildup and deposition on the surfaces of internal components of the reformer assemblies. Carbon buildup will clog the gas passages of the reformer ultimately, and will limit the effective service life of the reformer and thus the fuel cell power plant assembly which includes the reformer. It would obviously be desirable to produce reformer assembly components, and a method for forming such components, which would result in a reformer assembly which would be resistant to carbon build-up on surfaces of the reformer.